Sorry not to have responded sooner,

Generally a hole is the sign of a real lean mixture, preignition problems, or some water in the fuel supply. They often occur in high rev applications with higher compression engines, but more often in turbo application. As a matter of fact, having a turbo on your motor for the sake of more performance generally will degrade the life cycle of the engine to around 33%, depending on what the waste gate pressure is set at, (boost). From what I've seen, Volvo turbos run around 200,000 before needing to be replaced. The same engines naturally aspirated will last up to a million miles if they are not abused.

With Volvos being as inexpensive to purchase used, I would buy a wrecked one with a good motor and change them out. Be careful about letting anyone sell you a rebuilt turbo block. There is not enough meat in the cylinder walls to handle the pressure if they are bored out.

Good Luck,

Big Harry